One of the reasons it has never taken off is that GUI editors and layout managers that have come out for the web (and there have been a few), have never quite gotten the code right. They would produce a page that looked like the designer... but with terribly written HTML/CSS. So web designers and developers prefer to make their own markup.
The deeper problem is that the tech industry is slow to get rid of HTML, even though HTML was created to exchange documents, and nowadays we mostly use it as a GUI for network software. See "The Problem With HTML":
HTML isn't the problem - declarative markup is a great way of doing GUI layout, non-web GUI frameworks tend to come up with alternatives that look similar. The problem is CSS, which is a fractal of bad design, broken at every level, from selectors to the box model.
CSS works fine for Text markup. The problem is you get two models one where the Browser picks where stuff goes depending on the browser and local settings, another where the designer makes that choice. You can't have both things exist at the same time, on top of that most designers don't know what they are doing.
It used to be conventional wisdom that using HTML as a layout system is wrong, you know. Because it wasn't meant to be one, and text content was supposed to be independent of the medium on which it is viewed. Well, at the time I had my doubts that it was going to work, but it was (and still is) a nice idea.
